Community-based forest management under REDD+ has been suggested as a promising mechanism to conserve forests and at the same time enhance living conditions of their inhabitants. In the buffer zone of the Yasuní National Park in Ecuador, we analyzed the spatial and institutional configuration of Common Property Management Regimes (CPMRs) of two indigenous groups (Shuar, Kichwa) and a group of Colonist cooperatives in their historical development. We used the Ostrom (1990) principles to assess land configuration and institutional arrangements for decision-making in the use of shared resources and analyzed the implications for REDD+ implementation.We found that CPMRs of the two studied indigenous groups are becoming increasingly similar to those of the Colonists as a result of agrarian reforms and legal frameworks for communal organization. The informal continuation of traditional forms of organization under (modern) formal structures and the overlap of de jure and de facto rights hinder efficient and transparent forest governance and REDD+ implementation. Spatial and institutional homogenization of CPMRs of various ethnic groups and privatization of farms inside CPMRs causes further forest fragmentation and impedes conservation goals.